// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
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//
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package com.google.protobuf;

/**
 * RawMessageInfo stores the same amount of information as {@link MessageInfo} but in a more compact
 * format.
 */
final class RawMessageInfo implements MessageInfo {

    private final MessageLite defaultInstance;

    /**
     * The compact format packs everything in a String object and a Object[] array. The String object
     * is encoded with field number, field type, hasbits offset, oneof index, etc., whereas the
     * Object[] array contains field references, class references, instance references, etc.
     *
     * <p>The String object encodes a sequence of integers into UTF-16 characters. For each int, it
     * will be encoding into 1 to 3 UTF-16 characters depending on its unsigned value:
     *
     * <ul>
     *   <li>1 char: [c1: 0x0000 - 0xD7FF] = int of the same value.
     *   <li>2 chars: [c1: 0xE000 - 0xFFFF], [c2: 0x0000 - 0xD7FF] = (c2 << 13) | (c1 & 0x1FFF)
     *   <li>3 chars: [c1: 0xE000 - 0xFFFF], [c2: 0xE000 - 0xFFFF], [c3: 0x0000 - 0xD7FF] = (c3 << 26)
     *       | ((c2 & 0x1FFF) << 13) | (c1 & 0x1FFF)
     * </ul>
     *
     * <p>Note that we don't use UTF-16 surrogate pairs [0xD800 - 0xDFFF] because they have to come in
     * pairs to form a valid UTF-16char sequence and don't help us encode values more efficiently.
     *
     * <p>The integer sequence encoded in the String object has the following layout:
     *
     * <ul>
     *   <li>[0]: flags, flags & 0x1 = is proto2?, flags & 0x2 = is message?.
     *   <li>[1]: field count, if 0, this is the end of the integer sequence and the corresponding
     *       Object[] array should be null.
     *   <li>[2]: oneof count
     *   <li>[3]: hasbits count, how many hasbits integers are generated.
     *   <li>[4]: min field number
     *   <li>[5]: max field number
     *   <li>[6]: total number of entries need to allocate
     *   <li>[7]: map field count
     *   <li>[8]: repeated field count, this doesn't include map fields.
     *   <li>[9]: size of checkInitialized array
     *   <li>[...]: field entries
     * </ul>
     *
     * <p>Each field entry starts with a field number and the field type:
     *
     * <ul>
     *   <li>[0]: field number
     *   <li>[1]: field type with extra bits:
     *       <ul>
     *         <li>v & 0xFF = field type as defined in the FieldType class
     *         <li>v & 0x0100 = is required?
     *         <li>v & 0x0200 = is checkUtf8?
     *         <li>v & 0x0400 = needs isInitialized check?
     *         <li>v & 0x0800 = is map field with proto2 enum value?
     *         <li>v & 0x1000 = supports presence checking?
     *       </ul>
     * </ul>
     * <p>
     * If the (singular) field supports presence checking:
     *
     * <ul>
     *   <li>[2]: hasbits offset
     * </ul>
     * <p>
     * If the field is in an oneof:
     *
     * <ul>
     *   <li>[2]: oneof index
     * </ul>
     * <p>
     * For other types, the field entry only has field number and field type.
     *
     * <p>The Object[] array has 3 sections:
     *
     * <ul>
     *   <li>---- oneof section ----
     *       <ul>
     *         <li>[0]: value field for oneof 1.
     *         <li>[1]: case field for oneof 1.
     *         <li>...
     *         <li>[.]: value field for oneof n.
     *         <li>[.]: case field for oneof n.
     *       </ul>
     *   <li>---- hasbits section ----
     *       <ul>
     *         <li>[.]: hasbits field 1
     *         <li>[.]: hasbits field 2
     *         <li>...
     *         <li>[.]: hasbits field n
     *       </ul>
     *   <li>---- field section ----
     *       <ul>
     *         <li>[...]: field entries
     *       </ul>
     * </ul>
     *
     * <p>In the Object[] array, field entries are ordered in the same way as field entries in the
     * String object. The size of each entry is determined by the field type.
     *
     * <ul>
     *   <li>Oneof field:
     *       <ul>
     *         <li>Oneof message field:
     *             <ul>
     *               <li>[0]: message class reference.
     *             </ul>
     *         <li>Oneof enum fieldin proto2:
     *             <ul>
     *               <li>[0]: EnumLiteMap
     *             </ul>
     *         <li>For all other oneof fields, field entry in the Object[] array is empty.
     *       </ul>
     *   <li>Repeated message field:
     *       <ul>
     *         <li>[0]: field reference
     *         <li>[1]: message class reference
     *       </ul>
     *   <li>Proto2 singular/repeated enum field:
     *       <ul>
     *         <li>[0]: field reference
     *         <li>[1]: EnumLiteMap
     *       </ul>
     *   <li>Map field with a proto2 enum value:
     *       <ul>
     *         <li>[0]: field reference
     *         <li>[1]: map default entry instance
     *         <li>[2]: EnumLiteMap
     *       </ul>
     *   <li>Map field with other value types:
     *       <ul>
     *         <li>[0]: field reference
     *         <li>[1]: map default entry instance
     *       </ul>
     *   <li>All other field type:
     *       <ul>
     *         <li>[0]: field reference
     *       </ul>
     * </ul>
     *
     * <p>In order to read the field info from this compact format, a reader needs to progress through
     * the String object and the Object[] array simultaneously.
     */
    private final String info;

    private final Object[] objects;
    private final int flags;

    RawMessageInfo(MessageLite defaultInstance, String info, Object[] objects) {
        this.defaultInstance = defaultInstance;
        this.info = info;
        this.objects = objects;
        int position = 0;
        int value = (int) info.charAt(position++);
        if (value < 0xD800) {
            flags = value;
        } else {
            int result = value & 0x1FFF;
            int shift = 13;
            while ((value = info.charAt(position++)) >= 0xD800) {
                result |= (value & 0x1FFF) << shift;
                shift += 13;
            }
            flags = result | (value << shift);
        }
    }

    String getStringInfo() {
        return info;
    }

    Object[] getObjects() {
        return objects;
    }

    @Override
    public MessageLite getDefaultInstance() {
        return defaultInstance;
    }

    @Override
    public ProtoSyntax getSyntax() {
        return (flags & 0x1) == 0x1 ? ProtoSyntax.PROTO2 : ProtoSyntax.PROTO3;
    }

    @Override
    public boolean isMessageSetWireFormat() {
        return (flags & 0x2) == 0x2;
    }
}
